This invention relates to electrical connectors and to electronic structures using such connectors. More specifically, the invention relates to the use of compliant pin-type contacts adapted for being securely positioned within an opening, e.g., a plated through hole (PTH), in an electronic structure such as a printed circuit board (PCB) to provide electrical connection between the structure""s circuitry and an external component, e.g., a pinned module.
Various forms of pin-type electrical contacts, including those of the compliant type designed for being inserted within various electrical structures such as PCBs and test heads are known in the art, with examples shown and described in the following publications.
In U.S. Pat. No. 5,129,830 (Krajewski et al), there is described a xe2x80x9cz-axisxe2x80x9d connector pin designed to interconnect a plurality of stacked PCBs, the connector being drawn through aligned openings in the PCBs and frictionally engaging the internal walls of such openings.
In U.S. Pat. No. 5,139,890 (Cowie et al), there is described an electrical xe2x80x9ccomponentxe2x80x9d such as a contact or relay in which the structure comprises a copper or copper alloy substrate having thereon a xe2x80x9cthickxe2x80x9d silver coating for resistance to oxidation and wear. A thin gold coating may also be added to further improve oxidation resistance, lubricity and to serve as a diffusion barrier.
In U.S. Pat. No. 5,147,227 (Yurko), a terminal pin is described for insertion within a plastic housing, the pin including two sets of outwardly projecting nibs each having a flat edge surface normal to the terminal""s axis so as to dig into the plastic material and secure the pin in position.
In U.S. Pat. No. 5,230,632 (Baumberger et al), there is defined an electrical contact and connector wherein the contact is comprised of a first, highly conductive element and a second, internal spring element secured along a common interface to the first element. The second element has a greater modulus of elasticity than that of the first element. Projecting ends of the first element expand vertically in opposing directions to interconnect external conductors, e.g., PCB contact pads. This patent is assigned to the same assignee as the present invention.
In U.S. Pat. No. 5,653,601 (Martucci et al), a two-part connector structure is described wherein one contact part is deemed a receptacle for the other contact part, called the terminal socket. The receptacle fits securely within a base opening while the terminal thereafter inserts within the receptacle""s central opening. The resulting connector is specifically designed for preventing solder wicking from conductor pads on the base.
In International Business Machine""s Technical Disclosure Bulletin (TDB) vol. 30, no. 11, April 1988 (Frutchey), there is described and illustrated a zero insertion force contact in which spaced bimetal strips located within a test head are designed for expanding and contracting to receive a pin inserted between the two.
As understood from the following, it is a significant object of this invention to provide a relatively small electrical contact designed for relatively easy insertion within a corresponding electronic component opening without adversely altering the internal walls of such an opening. Being relatively small ensures that a plurality of such contacts can be utilized in a high density format, which is so much desired in today""s electrical component field. It is believed that such a contact and associated structure which overcomes various problems associated with prior art connectors/contacts, such as severe opening wall deformation, insufficient frictional force application (to assure positive securement), increased insertion forces (especially when seating a large number of closely positioned contacts), etc. would constitute a significant advancement in the art.
It is a primary object of the present invention to enhance the art of electrical connectors and particularly the art of connectors which use contacts of the compliant type designed for being securely positioned within openings such as those in PCBs.
It is another object of the invention to provide a connector contact of the above type which can be readily positioned within a plurality of such PCB openings with no (zero) insertion force needed.
It is yet another object of the invention to provide such a zero insertion force connector contact which can be so positioned in a relatively dense array while assuring positive electrical connections to the various conductors associated with the PCB and external component.
In accordance with one aspect of the invention, there is provided an electrical contact comprising a first layer of material having a first coefficient of thermal expansion, and a second layer of material bonded to the first layer of material along a common interface and having a second coefficient of thermal expansion different than the first coefficient of thermal expansion. The contact includes a first outer diameter at a first temperature less than the first inner diameter of an opening located in a circuitized substrate in which the contact is adapted for being positioned and is expandable to at least the first inner diameter at a second temperature different than the first temperature when the contact is positioned within the opening so as to engage the wall of the opening to provide a secure fit within the opening of the circuitized substrate.
In accordance with another aspect of the invention, there is provided a circuit assembly comprising a circuitized substrate having an opening therein of a first inner diameter, an electrical component including a housing and at least one electrical contact projecting from the housing and adapted for being securedly positioned within the opening, the electrical contact including a first layer of material having a first coefficient of thermal expansion and a second layer of material bonded to the first layer of material along a common interface and having a second coefficient of thermal expansion different than the first coefficient of thermal expansion. The contact includes a first outer diameter at a first temperature less than the first inner diameter in the circuitized substrate and is expandable to at least the first inner diameter at a second temperature different than the first temperature when the contact is positioned within the opening so as to engage the wall of the opening to provide a secure fit within the opening of the circuitized substrate.